Liquid urea-formaldehyde



'Reissued Nov. 29, 1949 LIQUID UREA-FORMALDEHYDE COMPO SITIONS Hemline M. .Kv lnc Wilm ngton, :DeL, assi nor to Elfin Pont deNemours and Gunman Wil- ,mington, DeL, .a corporation of Delaware No Drawing. Original No...2,46,'7,212, 'daiedApril 12, 1949, Serial No. '732,9 2f-7,,,March 6, 19517. Applicationfor reissue September '24, 19.49, Serial :9 Claims.

This invention relates to liquid, unpolymerized urea-*formaide-hyde reaction products and more particularly to liquid compositions comprising highly stable 'methylolureas and methods ior'preparingthesame.

Heretofore, it was -well'known that by reaction between urea and aqueous formaldehyde (usually in the presence-of an alkaline buffer) methylolureas, such as monomethylolurea, dimethylolurea, and mixtures of monomethylolurea and di- -methylolurea could be obtained. These unpol- *ymerized monometh-yloland d-imet-hylolureas were crystalline bodies which did not dissolve in all proportions in water and which did not yield permanently stable aqueous solutions. In general, aqueoussolutions of monomethylolor dimethyl- 'olurea, even in the presence of neutral or slightly alkaline buliers, developed 'opalescence --upon-storage-ior a relatively short-time especially at elevated temperatures. More prolonged storage generally resulted in the "formation of precipitates and the partial resinification of the methylolureas. This characteristic property of monomethylolurea and dimethylolurea limited to some extent the usefulness of these substances, especially in commercial applications requiring clear, permanently stable, urea-formaldehyde in relatively concentrated liquid form. Attempts have been made in-the past to "prepare methylolureas having a "higher formaldchydez urea ratio than dimethy-lolurea, but no instance has a :compound corresponding :to tetramethylolurea or trimethylolurea been isolated. Moreover, it lhasvgenerally not-been possible here- .toiore to prepare lat .ordinary temperature .unmesinified methylolureas in :sufiiciently high con- :centration to permit their use .:a-s impregnating agents in processes requiring a veryhighly concentrated liquid urea-formaldehydereagent.

An object of this invention is to provide a .stable, liquid urea-formaldehyde reaction prod- .uct in an unpolymerized form. .Anotherobject of theinvention is to provide a process .ior the preparation of liquid, permanently stable, .unpolymerized urea-formaldehyde compositions which are high in content of resin-forming ingredients, and which are suitable for shipment in commercial tank car equipment. Other objects of the invention will appear hereinafter.

The objects of this inventionare accomplished as a result ofa combination of discoverieaall of which contribute to the extraordinary results achieved. One of the discoveries embodied in the present invention is the observation that when mixtures of gaseous .formaldehyde and Water vapor at elevated temperatures are cooled to about 60 to 90 C. (suitably by absorption in a circulating formaldehyde-water mixture having a formaldehyde and water content about the 2 same as that of the absorbed gases) the resulting molten mixture containing more than-50% by weight of formaldehyde '(such mixtures being --solid at ordinarytemperature) has significantly difierent chemical properties if maintained continuously at a temperature above 60 -C.-tha-n it has if permitted to cool-down somewhat below 60 C. This chemical or physical change of-the iormaldehyde in the resulting aqueous formaldeversi-ble; i.

hyde mixture "upon cooling below 60 is not ree., when theliquid or solidmixture is subsequently reheated to a temperature of -60" C. to 90 -C.-the formaldehyde does not reacquire the characteristics which are essential in the preparation of the reaction products hereinafter described. "It has been discovered in accordance with this inventionthat when an aqueous liquid,

prepared from gaseous formaldehyde and water at a temperature of 60 to 90 (3. in the proportions necessary to form a molten -mixture con- -tai-ning*50% -to'70% by weight of formaldehyde, is reacted with urea '(the relative quantities are disclosed hereinafter) ata pH within the range of Z .0 to "9.0, and the temperature of "the mixture is thereaftermaintained at least momentarily at from it? to "90 'C., a permanently stable clear liquid product is obtained, provided the molten aqueous formaldehyde mixture is kept continu- 'mixing the same with urea.

ousl-y at a temperature above 69 0. prior to ad- "If :a similarly prepared'aqueous'rormaldehyde ofthe same strength is {permitted to cool-to a temperature below 160 C. before the reaction "with urea, a liquid composition -which develops opalescence upon storage is obtained. A brief cooling to a temperature not below about 455 C.-;frequently can be tolerated, but this is always a dangerous practice, since complete assurance against development of opalescence is highly important in commercial practice.

It has'also been discoveredin'accordance with this invention that the initial mol ratio of 'formaldehyde to urea :is highly critical :in "the pronotion of the clear, 'stable,-liquid products above described, containing, in preferred embodiments,

about-'60 to% by Weight of urea-formaldehyde.

"When'the initial mol ratio ofiormaldehydemrea is below about 319, the process o'f the invention does not give rise to products which have the stability which is desirable in commercial applications but to Products which developcloudiness upon storage. However, when theinitial mol ratio of formaldehydeaurea is about -,6'..Q, vvthe process above described yields perman ntly stable, clear, When .the initial .rnol ratio .of

1,051, the reaction .productdoes not remain per- ,manently clear except {at .temperaturesin excess of 50 C.; if the said reaction product is cooled aldehyde from the scrubber.

below 50 C., a precipitate develops. However, if the urea is added to the reaction mixture in two stages, the initial mol ratio in the first stage being from about 5.5:1 to about :1, and the mol ratio of total formaldehyde to total urea being finally not less than 4.521, nor more than 7:1, permanently stable, clear, liquid compositions which do not form precipitates at room temperature or at temperatures encountered under ordinary storage conditions are obtained. The preferred liquid compositions, prepared by either the onestage or two-stage embodiments of the invention, contain formaldehyde and urea in the mol proportions of from 4.5:1 to 7:1, since they remain clear liquids when cooled to about 25 C.

The liquid compositions of this invention evidently contain higher methylolureas and free formaldehyde, the free formaldehyde being stabilized at such a stage of polymerization that it tends to solubilize the methylolureas and does not tend to form precipitates of paraformaldehyde or other relatively insoluble formaldehyde polymers. These liquid compositions difier from acidic ureaformaldehyde mixtures as prepared by previously known procedures which contain very little free formaldehyde, and which contain the uron ring. The preferred compositions of this invention are miscible with Water in all proportions and are generally water clear, lirnpid liquids. They have the consistency and appearance of other unpolymerized organic liquids, such as ethylene glycol. These preferred compositions are rich in free formaldehyde, the mol ratio of combinediormaldehyde to free formaldehyde therein being about 1:1 to 3:1. It is indeed highly surprising that normally liquid compositions which do not develop cloudiness can be prepared by mixing a normally solid aqueous formaldehyde composition with solid crystalline urea.

In the preparation of these clear liquid compositions, it is highly essential that the pH be carefully controlled since even slight deviation from the pH range of 7.0 to 9.0 gives rise to products which develop opalescence. A definite optimum clarity and stability of these liquid products is encountered at a pI-I of 8. It is generally preferred to adjust the pH of the aqueous formaldehyde prior to admixing the aqueous formaldehyde with the urea. Sodium or potassium hydroxide may be used as the sole agent for controlling alkalinity, but alkaline buffers are preferred. At any pH above 9 polymerization of the formaldehyde occurs in the absence of urea. The longer the time during which such polymerization occurs, the less stable is the urea-formaldehyde liquid product which is prepared therefrom.

In one embodiment of the invention, moist gaseous formaldehyde which has been maintained at a temperature above 60 C. and which, in fact, is directly piped (while still hot) from the plant for manufacturing formaldehyde from methanol, is admixed with an additional small quantity of water until a composition containing about 60% formaldehyde is obtained. In practice, it is convenient to effect rapid cooling of the hot vapors in a scrubber through which is circulated cooled 60% formaldehyde. In this embodiment the moist gaseous formaldehyde, prior to absorption, usually contains the stoichiometric quantities of formaldehyde and water which are produced by methanol oxidation, so that no more than a few percent of water should be added. One reason for adding this water is to control accurately the concentration of form- Substantially no methanol is present in the product. The temperature of the resulting aqueous formaldehyde is kept above 60 C. until urea is admixed therewith. Usually the aqueous formaldehyde mixture as first prepared has a pH of about 3. A convenient method for adjusting this pH to 7.0-9.0 is to treat the said aqueous formaldehyde (at a temperature exceeding 60 C.) with a suflicient quantity of phosphoric acid and sodium hydroxide to produce the desired pH. Any other buffer mixture which produces this p-H may be employed; for example, mixtures of sodium hydroxide and boric acid, or other similar buffer mixtures, give substantially the same results as are obtained with the phosphoric acid-sodium hydroxide buffer.

The table presented in Example I illustrates several embodiments of the invention and demonstrates the critical efiect of lowering the formaldehydezurea ratio below about 3.9 or raising this ratio above about 7.0. In this table, the color of the liquid reaction product is reported in terms of a color scale in which water white is assigned a value of 2, which corresponds to 0.003 grams of potassium clichromate per liter of distilled water. The F/U ratio is the mol ratio of total formaldehyde to total urea, i. e. it includes the free and combined reactants. The opaque point reported in the table is the temperature at which a clear urea-formaldehyde liquid becomes cloudy upon chilling a sample thereof (about 10 ml.) with stirring in a test tube having a diameter of about one inch; the cooling of the sample is accomplished by intermittent dipping in acetone-Dry Ice mixture. Tests 1(0), 1(d) and 1(e) in Table 1 represent preferred embodiments of the process of this invention.

In one method of practicing the invention, the initial mol ratio of formaldehydezurea may be above about 5:1 and as high as about 10:1. However, the use of very high ratios (e. g., 10: 1) is disadvantageous because while the resultant products remain liquid when cooled to about 50 C., they do not remain liquid when cooled below 50 C. Additional quantities of urea may be added to such mixtures to produce a permanently stable liquid product having any desired ratio of formaldehydezurea within the range of about 4.5:1 to about 7:1. It is, however, preferred to prepare the permanently stable mixture having an F/U ratio of about 6 directly. This, of course, permits subsequent adjustment of the F/U ratio to any desired value by addition of urea to the mixture having an F/U ratio of 6.

The invention may be practiced by preparing an aqueous liquid mixture from the herein disclosed quantities of gaseous formaldehyde and water at 60 to C. by any convenient method Whatever, and suitably by liquefying a gaseous formaldehyde water-vapor mixture having a temperature above 90 C. and containing about 50% to 70% by weight of formaldehyde by cooling the said aqueous liquid mixture to a temperature of 60 to 90 0., keeping the temperature of the said aqueous liquid mixture substantially continuously above 45 C., and preferably above 60 C. until the said liquid is brought into contact with urea, admixing urea with the said liquid in the presence of a buffer which maintains the pH within the range of 7.0 to 9.0, the amount of the said urea being preferably in the proportion of one mol per 4.5 to 10 mols of the said formaldehyde, and maintaining the temperature of the e rl-.14

resultantliquid --at-least momontarily...(i;- -e. -for oneor two minutes at -a temperature 01 HOLto 90 C. whereby a product-which remainsea clear liquid when cooled tOz-509-Ce-1S obtained-w In. specific embodiments-the initialmol ratio of formal- .dehyde urea s-houldbefrom about 4.5-to 7.0; if a reaction product which-1'remainsawlear liquid when cooled to.roomtemperatureland in fact well 7 below room temperature). --is desiredl-- The optimum initial mol ratio of formaldehydem-rea .forpermanent .stability' is 6 :1. 1 In-particular embodiments of theinventi on-,-. the clear liquid initially obtainedasabovee'described mayaa be treated With-additional amountsiofurea tobring the formaldehyde ureac ratio down to as low I as about 3.9 the resultant products-- are still stab1e,

clear liquids. The temperature of-the mixture is additions of ureato the'mixtures'having'an F/U ratio of .4 to 6, whereby. .reactionmixtures containing free formaldehyde and monomethylol and/or: dimethylolureas ane-formed: The latter step is generally 1: erformed. immediately prior to actual use of the urea formaldehyde composition (e.- g.; as an impregnating-agent). -In this man- .ner it is possible to avoid-the formation of precipitates or polymeric products prematurely in urea:formaldehyde compositions comprising monomethylol and/r dimethylolurea': It thusbecomes possible for theproducer' ofthe chemical 10 to ship the-permanently stable composition having-an F/U ratio-of 4 to 6 in tank cars, and for the-resin manufacturer to adjust the F/U ratio of the mixture to the desired-value by addition of ureashortlybefore the resin-forming composi- ;tion is to be used.

The invention'is illustrated by means of the following examples which-show thepreparation of a clear, stable, liquid urea-formaldehyde reaction product in which 'the formaldehyde component prior toreaction withurea'is'in the form of an aqueousmolten mixture which has been maintained continuously at a temperature above about C. from the time'of its-formation from gaseous formaldehyde andwatervapor-at to 90 C.

25 until the-time of its reaction with urea. The examples also demonstrateseveral of the important differences between the composition and process of the present invention,= and previously known compositions and processes.

0 Example I.The-following=table records" in detail several comparative experiments which i'llus =trate the process of the invention.

7 TABLE 1 Preparation of liquid urea-formaldehyde products Test number 1(a)- 1(b) 1 (c) 1 (d) 1 (41) 1 (f) HCHO soln, g 1, 000 984 97 6 976 1, 000 500 HCHO, Wt per 60 61.0- 6115 61:5 .60' i 60 ECHO, e00 600 e00 e00 600 300 HQHO, mo1es 20 '20 20 20 20 10 Temp. when buffered, C 62 80 76 75 Buffer I aPO 1MHaP04 '1MH3104 0.5MH3B O3 0.5MH BO 1MH P0 .Amt. of buffer, m1 8 8 16 16 2 Amt. oi 2.5N-NaOH, m1 16 16 16 16 16 7 1st Urea'additflm 1 Time, mins. from bufiering 4 g 3 6 3 3 l 58 ea 65 65' 65 65 200 0D 1 200 200 20 3.33 3. 33 3 33 3.33 3 33 1. 25 6 6 6 6 p 8 87 89 86 73 Water addifivm Temp. when H20 added, C 79. 5 l 25 86.5 4 88. 5 Amt; 1120.added, g 41 36 .34 l

2nd Urea addition 7 Time, minsirom bufieringn 14 1 0a. 1, 000 13 Temp, C 50 25 .50 Uree, g 143 108 Total urea additilm Urea, g 343 308 300 300 "200'- 75 Urea, moles 6. 71 5.13 5 5 3. 33 1; 25

Opaque Clear --Clear; Clear 3.5 -3.9 I 4.0 4.0

6 7 67 .67 12. 3 13. 4 l3. 3 I 31. 9 31. 4 31. 2 Total HCHO, per cent 42.15 44. 8 .4455 Urea, per cent 8 24.3 22. 7; 22. 4. v22. 2 Combined ECHO/free HGHO... 2. 6 2. 2 2. 3' Color 1- 1 I 1 Water miscibility. Complete Complete p11 7.8 8.0 8.6 Sp. gr. 60 F./60 F 1.268 1. 261 1.259 R. I. at 25 C. (refractive 1ndex).. 1.447 1.443 1. 442 Opaque point, C "-24 24 -22 Viscosity, cp. at 100 F 14 13 14 1 Water and second urea addition on day following; preparation of F/U 6; 2 Properties of the product are for material'aged 1 month except as noted otherwise.

3 Based upon the wei ht of the starting materislsw Q When prepared. '1 6 glass electrode method-swarmed."

Example II.A sample of 60% formaldehyde similar to the material used in the tests of Table 1 was stored at room temperature for 6 days. The solid formaldehyde was then heated to 75 C. and a urea:formaldehyde composition having a formaldehydezurea ratio of 4 was prepared using the same procedure as is described in test 1(0) of Table l. The buffered aqueous formaldehyde mixture at 75 C. was liquid but opaque. However, on making the first urea addition at 65 C. the temperature rose, and the mixture became clear. The resultant liquid urea:formaldehyde reaction mixture remained clear when cooled to room temperature; however, in contrast with the product obtained in test 1(0) this liquid product became opalescent on storage at room temperature for two days. Further storage of the mixture for a period of one month caused the formation of a considerable precipitate.

This example illustrates the fact that the change in the formaldehyde properties upon cooling is not reversible upon simple reheating to 75 C. Once the formaldehyde has been converted to the form which is produced by cooling, mere reheating to the reaction temperature does not reconvert it to the form needed for the preparation of the permanently stable (1. e., clear) urea-formaldehyde products.

Example IIL-A sample of the liquid ureaformaldehyde composition having a formaldehyde to urea ratio of 6 was prepared by the procedure of test 1(a) of Table 1, except that the formaldehyde mixture initially contained 63.5%

HCHO, and the pH of the formaldehyde was ad justed to 9 prior to adding the urea. The resulting liquid product (urea-formaldehyde content, 70%) was cooled to room temperature and stored for a period of 14 weeks at which time the test was terminated. The product remained liquid entirel clear throughout this period.

Example IV.Samples having a formaldehyde: urea ratio of 8 (cf. Example III, in which a very stable product was obtained when the F/U ratio' was 6) were prepared using the procedure illustrated in test 0) of Table 1, except that the pH of the aqueous formaldehyde was adjusted as set forth below. The table records the effect of pH of the formaldehyde on the clarity of the products.

TABLE 2 Effect of pH on clarity of product at an F/ U ratio of 8 Test number 2 (a) 2 (b) 2 (0) Clarity of Product (1) Aged 1 day at room temp (2) Aged 2 days at room temp cloudy opaque clear opaque cloudy opaque dehyde in this mixture was 7.43% of the totalweight of the mixture and the ratio of combined formaldehyde to free formaldehyde was 5.82. The

' Testnumber pH of the product was 7.3. In-a second preparation using the above procedure the reaction mixture was left on the steam bath for 22 hours. A cloudy liquid product which could not be filtered except by suction was obtained.

' This example illustrates the fact that the procedure described in the literature for the preparation of higher methylolureas (and products obtained therefrom such as uron ethers) is not applicable for the preparation of clear, stable liquid products which are obtained in accordance with the present invention.

Example VI.--To' 100 grams of the reaction product obtained in accordance with the process described in test '1 (d) in Table 1 was added a solution containing'22.3 grams of urea and 768 grams of water. The resulting product, which initiall had a free formaldehyde content of 2.7%, was heated at the temperature set forth below. This caused the free formaldehyde in the mixture to react with urea forming a solution in which the ratio of combined formaldehydezcombined urea was '2. The rate of the reaction of the free formaldehy'de'with urea is shown in the following table.

TABLE Free Formaldehyde Elapsed Time Temp.

0 minutes 10 minutes 30 minutes Percent NIN I The reaction product thus obtained was an aqueous solution of methylolurea which evidently was substantially'all in the form of dimethylolurea.

Example VII.The following table illustrates the formation of clear, stable urea-formaldehyde compositions when the total quantity of ureaformaldehyde (including free and combined formaldehyde) is to of the weight of the reaction product, the F/U ratio in the final products being 4:1.

TABLE '4' M Preparation of liquid urea-formaldehyde products [Urea-Formaldehyde Content 60 %-B5%] 4 (d) 4 (b) 1 (c) Formaldehyde HOHO soln. g HOHO, wt. per cent. HCHO Temp. when buffered, 0

lM-HgP Limit. of buffer, ml Amt. of 2.5N--NaOH, ml.

1st Urea Addition Time, from buffering...

Water Addition Temp. when H20 added, 0.- Amt. H|0 added, g

--fIAsr.rr4-Continued Test number 4 (a) 4 (b) 4 (c) 2nd UrewAddiiion Time,-mins; from hollering. 20 13 11 l-ernp 50 50 v 50 Urea, g 100 100 100 Total Urea Addition Urea; g. ..i 300 300 300 Urea, mols 5 5 Product Clarity, Clear Clear Clear FU. 4.0 4.0 4.0 Total non-aqueous ingred,

per cent 3. 59. 8 62. 4 64; 8 Free ECHO, per cent. 13. 4 13. 3 13. 5 Combined HOBO, per 0 26. 3 28. 2 20. 5 TotalHQHO per cent 2 39; 7 41. 5 43. 0 Urea. per cent 20.1 20. 9 21. 8 Combined H CH O/fr ee HQHO 2.0 2. 1 2. 2 1 1 1 Comple e Complete Complete 11 8.3 8.9 as Sp gr,,60 F./60 F". 1. 234 1.243 1. 252 Refractive index at 25 C 1. 4315 1. 4351 1. 4394 Properties of the product are {or material aged 2 months except as noted otherwise.

1 Basedupon the weights of the starting materials.

-When prepared.

Example VIII.--Example III was repeated except; that the second addition of urea was made at a temperature-of 81 C. i. e. the mixture was not cooledto 50 C. prior. to the second addition of urea. The. resulting product, having an F/U ratio. of 4} and a total urea-formaldehyde (free andcombined) content of 70%, was not stable, but contained a precipitate after two Weeks storage at room temperature.

This example illustrates the advantages which resultfrcm cooling the mixture to 50 C. (or below) prior to the second addition of urea.

The above examples serve to illustrate the invention, and'to distinguish it from prior methods, especially such prior methods as fail to em-,

ploy the particular formaldehyde composition herein disclosed.

The aqueous formaldehyde which is employed as a reactant in the practice of this invention is water clear, and may be prepared by dissolving gaseous formaldehyde in water at 60 to 100 C. Inapre'ferred embodiment a gaseous formalde hyde-water vapor mixture obtained by methanol oxidation is cooledto about 60 to 90 C. by adsorption in a circulating molten mixture of formaldehyde. and'water containing about 60% formaldehyde. This causes an increase in the volume' of the "molten mass containing about 60%-' to,63%[iformaldehyde, the remainder of the moltenjmass being water and a minutev trace of formic acid. Any necessary adjustment of the water content can be made by subsequent introduction of Water at a temperature in excess.

of 60 C. Water should not be added at a lower temperature, because, as explained above, the aqueous formaldehyde should be kept at 60 to 90J'at allttimes -prior to admixing it with urea.

The apparatus employed in preparing the ureaformaldehyde compositionsof this invention may be any appropriate reaction vessel, equipped-with means for agitating the reaction mixture and means for controlling the reaction temperature.

An ordinary,stirred kettlevinto which the molten formaldehyde and solid urea can be conducted is preferred. A trap door, constitutes a suitable means for introducing the urea into the molten buifered formaldehyde mixture, or for subsequent additions of urea as above described. These subsequent additions of urea may be madein the same reaction vessel, or in a similar vessel, which may, for example, be located at a distant point. Thus, the initial addition of urea may be in the proportion of 1 mol to from 5 to '7 mols of formaldehyde. The subsequent addition of urea, whereby the total formaldehydezurea ratio may be adjusted, for example, to a value which is less than 5 and greater than 1, can be made in very simple equipment, because of the fact that urea is very readily soluble in the initial liquid reaction product.

'The liquid compositions of this invention differ fromprior compositions in several different respects, and, in particular, are characterized by the following properties, and numerous others: (1) "absence of uron ring. which is present-in acid-treated mixtures having a high F/U ratio, (2) specific ratio of combined formaldehyde to free permanently soluble formaldehyde, which results in permanent clarity, (3) low opaque point, (4) low viscosity at high concentration of nonaqueous ingredients (high solids content). To obtain permanently clear products at a solids content of to or higher ("solids-content meaning the free and combined urea and HCHO), it is highly important that the compositions have the correct ratio of combined formaldehyde to free formaldehyde as herein specified. By the use of the process herein described for preparing permanently stable liquids this ratio varies from about 1:1 to 3:1,when the F/U ratio is 4:1 to 6:1; at an F/U ratio of 6:1, the ratio of combined formaldehyde to free formaldehyde is usually between 1.0 and 1.8, while at an F/U ratio of 4-:L-theratio of combined formaldehyde to free formaldehyde is usually between 1.8 and 3.0.

'The free formaldehyde referred to throughout this specification can be measured analytical- 1y by any appropriate method, such as by the neutral sulfiteprocedure at 0 C.

The liquid products of this invention are widely useful in the preparation of impregnating agents, lacquers, molded products, finishes, etc. They are especially valuable in the process for impregnating wood, saw dust, wood flour, grasses, jute, hemp, rattan, reeds, palmetto, Masonite, bagasse, and other forms of lignocellulosic and cellulosic materials, describedin detail in copending application S. N. 555,042, filed September 20, 1944, of which the present application is a continuation-in-part, and the parent application S -N. 478.666, filedMarch 10, 1943 (now U. S. Patent 2,398,649), and for the preparation of very dense that-the product obtainedby cooling the mixturev to a temperature of 50 C. is a clear liquid. vThe said liquid, however, is not permanently clearbut becomes an opaque solid quite rapidlygespecially when cooled to 25? C. In general, the methylolureas prepared by thev processpf .U. ;S.;.Pat ent- 2,321,544 cannot be obtained in the form of concentrated liquids which remain permanently clear and stable at ordinary temperatures.

hyde and water at a temperature of 60 to 90 C.,.

the weight of formaldehyde being from 0% to 70% of the weight of the resultant aqueous liquid mixture, keeping the temperature of the said aqueous liquid continuously above 45 C. until the said liquid is brought into contact with urea, admixing urea with the said liquid at a pH within the range of 7.0 to 9.0, the amount of the said urea being in the proportion of one mol per 4.5 to mols of the said formaldehyde, and maintaining the temperature of the resultant liquid at least momentarily at from 70 to 90 0., whereby a product which remains a clear liquid when cooled to 50 C. is obtained.

2. A process for the preparation of liquid ureaformaldehyde compositions which comprises preparing a liquid mixture from gaseous formaldehyde and water at a temperature of from 60 to 90 C., the weight of the formaldehyde being from 50% to 70% of the weight of the resultant aqueous liquid mixture, keeping the temperature of the said aqueous liquid continuously at 60 to 90 C. until the said liquid is brought into contact With urea, admixing urea with the said liquid in the presence of a bufier which maintains the pH within the range of 7.0 to 9.0, the amount of the said urea being in the proportion Of one mol per 4.5 to 7 mols of the said formaldehyde, and maintaining the temperature of the resultant liquid at least momentarily at from 70 to 90 C. whereby a product which remains a clear liquid when cooled to C. is obtained.

3. A process for the preparation of liquid ureaformaldehyde compositions which comprises liquefying a mixture of gaseous formaldehyde and water-vapor having a temperature above 90 C. by cooling to a temperature of 60 to 90 C., the weight of formaldehyde being about 60% 0f the weight of the resultant aqueous liquid, keeping the temperature of the said aqueous liquid continuously above 60 C. until the said liquid is brought into contact with urea, admixing urea in a stirred kettle with the said liquid in the presence of a buffer which maintains the pH within the range of 7.0 to 9.0, the amount of the said urea being in proportion to 1 mol per 6 mols of the said formaldehyde, and maintaining the temperature of the resultant liquid for about'two minutes at a temperature of from 70 to 90 0., whereby a product which remains a permanently clear liquid when cooled to below 25 C. is obtained.

4. A process for the preparation of liquid ureaformaldehyde compositions which comprises liquefying a, mixture of gaseous formaldehyde and water-vapor having a temperature above 90 C. by cooling to a temperature of 60 to 90 C., the weight of formaldehyde being from to 70% of the weight of the resultant aqueous liquid, keeping the temperature of the said aqueous liquid substantially continuously above 60 C. until the said liquid is brought into contact with urea, admixing urea with the said liquid in the presence of a buffer which maintains the pH within the range of 7.0 to 9.0, the amount of the said urea being in the proportion to 1 mol per 6 mols of the said formaldehyde, and maintaining the temperature of the resultant liquid at least momentarily at a temperature of from 70 to 90 (2.,

12 whereby a solution which remains a permanently clear liquid when cooled to 25 C. is obtained cooling the said solution to a temperature not exceeding about 50" 0., thereafter admixing an additional quantity of urea with the said solu-- tion in such proportions that the mol ratio of formaldehydemrea is not less than 3.9 to 1, whereby a, product which remains a clear liquid when cooled to 25 C. is obtained.

5. A process for the preparation of liquid ureaformaldehyde compositions which comprises liquefying a mixture of gaseous formaldehyde and water-vapor having a temperature above 90 C. by cooling to a temperature of to 90 the weight of formaldehyde being about 60% of the weight of the resultant aqueous liquid, keeping the temperature of the said liquid continuously from 60 to 90 C. until the said liquid is brought into contact with urea, admixing urea with the said liquid in a stirred kettle in the presence of a buffer which maintains the pH within the range of 7.0 to 9.0, the amount of the said urea being in the proportion of 1 mol per 5 to 7 mols of formaldehyde, cooling the resultant permanently clear liquid mixture to below 50 0., and thereafter adjusting the total formaldehydemrea ratio to a value less than 5 and greater than. 1 by addin urea to the said liquid mixture.

, 6. In the process set forth. in claim 5 the step which comprises adjusting the final formaldehyde:urea ratio to between 1:1 and 2:1.

7. A clear, permanently stable, liquid unpolymerized urea-formaldehyde composition containing a buffer which maintains the pH at from 7.0 to 9.0, said composition being characterized in that it has a total formaldehydefur'ea mot ratio of from about 4:1 to 6:1, and a ratio of combined to free formaldehyde of from 1:1 to 3:1, said composition having been preparedi in accordance with the process of claim 2.

8. A clear, permanently stable, liquid unpolymerized urea-formaldehyde composition containing a buffer which maintains the pH at from 7.8 to 8.6, said composition being characterized in that it has a total fonnaldehydezurea mol ratio of 4:1, a ratio of combined to free formaldehyde of from about 2.221 to about 2.611, a re fractive index of about 1.442 to about 1.447, and: a solids content, based on total urea and formalde hyde present, of about 67%, said composition. having been prepared in accordance with the process of claim 4.

9. A clear, permanently stable, liquid unpoly-- merized urea-formaldehyde composition having a pH of 7.0 to 9.0, said composition being characterized in that it has a total formaldehydezurea mol ratio of about 6:1, a ratio of combined to free formaldehyde of about 1.33, refractive index of about 1.7443, and a urea-formaldehyde content, based on total urea and formaldehyde present both free and combined, of about said composition having been prepared in accordance with the process of claim 2.

HAMLINE M. KVALNES.

Name Date Dittmar et al. June 8, 1943 Number 

